resolves #824 BOM in file confuses parser

This commit modifies Reader to strip a leading byte order mark. Instances of U+FEFF that are not the first character are not modified, since they are not byte order marks.

I added tests for both cases, even though the second test passed initially, since it preserves the existing behavior. I've tested this in an actual document as well and it appears to work correctly.

This resolves issue #824.